Atomic spectrochemical analysis has been routinely carried out by determining the appropriate solvent, dissolving the sample to be analyzed and injecting the solution into an atomizer using a nebulizer to form an aerosol containing the sample. The aerosol particles are then treated to give spectroscopic indication of the atomic constituents present. The procedure of dissolving can produce background interference unless appropriate solvents and procedures are used. Accordingly, sample preparation has been generally a time consuming and tedious task. Also, many materials are not amenable to conversion to a stable solution, e.g. oxides, carbides, nitrides, and others. It has been appreciated in the prior art that it would be beneficial, more convenient and less expensive to provide an apparatus and methods for introducing solid samples directly into spectrometers without the dissolving step. One technique that has been employed is to use electrical discharge for the production of aerosols containing particles from conducting and nonconducting materials. Versions of this technique employ a high voltage spark and involve control of the spark voltage and current waveforms.
Sparks having short pulse widths, high repetition rate and high energy are known to produce finer particles and provide more reproducible sampling. It has also been known to employ very high voltage, short duration pulses to ionize an air gap between a sample and an electrode and then to provide one or more controlled current-waveform pulses of adequate duration to produce particles to make the aerosol. One paper reporting such an approach is Mohamed, et al., Direct Sample Introduction of Solid Material into a Pulse Operation MIP, Appl. Spectrsc., Vol 43, No. 5, pp. 793 (1989).
The current methods and apparatus for producing particles directly from a solid sample by spark ablation are not able to provide the same precision and accuracy as the older more ti me consuming dissolution/nebulization techniques. Accordingly, there is a need for more efficient and less costly but improved methods and apparatus for direct solid sampling.